The thalamocortical and corticothalamic pathways of the visual system will be studied in normal cats, tree shrews and squirrels, and in individuals that have been raised with one eye sutured. Changes that occur in the dorsal lateral geniculate nucleus and in the visual cortex following partial visual deprivation will be studied by light and electronmicroscopical methods. In addition, a systematic study of the corticofugal pathways of the visual system will be initiated, and this will concentrate especially upon thalamic and tectal terminations.